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Using in situ resistance measurements on diamond anvil cell, we have monitored the pressure and temperature dependence of the CaB6 electronic transport properties. We report that CaB6 is a semiconductor at room temperature and at ambient pressure, in contrast to previous studies suggesting a semimetal nature. From ambient pressure to 12 GPa, the CaB6 conductivity smoothly increases, and CaB6 behaves as a semiconductor, although the CaB6 conductivity shows a metallic temperature dependence over a temperature interval ranging from 110 to 300 K due to its extrinsic region (where an increase in the temperature produces no effect on the CaB6 sample carrier densities and the CaB6 conductivity is, therefore, solely determined by the carrier mobilities). At around 12.4 GPa, CaB6 undergoes a metalliclike transition leading to a change in the CaB6 conductivity by a factor exceeding three orders of magnitude. This large increase in the CaB6 conductivity has been interpreted as resulting from an overlap between the conduction band and the valence band. From 12.4 to 26 GPa, the CaB6 conductivity markedly increases and is similar to a metallic one. [ABSTRACT FROM AUTHOR]

Using in situ resistance measurements on diamond anvil cell, we have monitored the pressure and temperature dependence of the CaB6 electronic transport properties. We report that CaB6 is a semiconductor at room temperature and at ambient pressure, in contrast to previous studies suggesting a semimetal nature. From ambient pressure to 12 GPa, the CaB6 conductivity smoothly increases, and CaB6 behaves as a semiconductor, although the CaB6 conductivity shows a metallic temperature dependence over a temperature interval ranging from 110 to 300 K due to its extrinsic region (where an increase in the temperature produces no effect on the CaB6 sample carrier densities and the CaB6 conductivity is, therefore, solely determined by the carrier mobilities). At around 12.4 GPa, CaB6 undergoes a metalliclike transition leading to a change in the CaB6 conductivity by a factor exceeding three orders of magnitude. This large increase in the CaB6 conductivity has been interpreted as resulting from an overlap between the conduction band and the valence band. From 12.4 to 26 GPa, the CaB6 conductivity markedly increases and is similar to a metallic one. [ABSTRACT FROM AUTHOR]

We have determined the unit-cell parameters of diaspore α-AlO(OH) at high pressures (13.5–27.8 GPa) and at high temperature (1900 K). Experimental data are compared with the theoretically predicted crystal structure variations derived from density functional theory (DFT) calculations. The experimental analysis establishes that the a axial direction is more compressible than the b and c axial directions in the low-pressure range (13.5–18 GPa) and at 1900 K, whereas all three directions show similar behaviors in the high-pressure range (18–27.8 GPa). The diaspore isothermal bulk modulus KT values are 137.6 GPa, 124.8 GPa, and 141.3 GPa, respectively, at 300 K, at 1900 K, and again at 300 K after quenching. By comparison, the diaspore isothermal bulk modulus KT computed at 300 K and at ambient pressure in the framework of the plane-wave pseudopotential approach is equal to 129.3 GPa. [ABSTRACT FROM AUTHOR]

We have prepared by electrodeposition nanoscale spin valves into the pores of anodic alumina membranes. Aligned nanometric spin valve arrays, well characterized by field emission scanning electron microscopy, are vertical with respect to the plane of the template and exhibit a perfect two-dimensional array with a hexagonal pattern. The largest value of room temperature giant magnetoresistance (GMR) we achieved is 6.8% at 75 Oe. The relatively low saturation fields together with relatively large GMR should make such structures attractive for sensor applications. [ABSTRACT FROM AUTHOR]